The techniques of microscopy and pharmacology will be used to investigate the role of the cell cortex in regulating cell division and cytodifferentiation in the ciliated protozoan Stentor coeruleus. That these processes are regulated in Stentor by events occurring within the cell cortex has been demonstrated using microsurgical manipulations for which this cell is uniquely suited. Such studies clearly show that three key events associated with division and cytodifferentiation are triggered by cortical signals. These events are: proliferation of a selected population of basal bodies; drastic shape change of the cell nucleus; and, cessation of DNA synthesis by the nucleus. The signals which trigger these events travel through the cytoplasm by means other than diffusion, indicating some type of Structural Information Transfer. Nothing is known of the structure(s) involved, the molecular mechanism by which information is transmitted through the structure, nor the means by which that information transfer is triggered by the cortex. Experiments are proposed here to begin to resolve these questions. Structural interconnections between the cortex and the nucleus and basal bodies will be sought using immunolabeling techniques at the light microscope level and electron microscopy for ultrastructural detail. A combined pharmacological/ultrastructural approach will be used to determine which structural interconnections found play a role in division and cytodifferentiation. Finally, we will initiate studies to determine if glycosylated components of the cell surface play a role in triggering information transfer. Using distribution of lectin receptors we will probe for changes in membrane topography which may occur commensurate with information transfer through the cortex to the structural interconnections. Depending on the results of these studies additional experiments will be designed to probe: the molecular mechanisms by which the cortex triggers structural information transfer; the mechanism by which that information is conveyed through the structural interconnections; and, how such signals lead to the responses evoked in the basal bodies (proliferation) and nucleus (shape change and cessation of DNA synthesis).